The present invention concerns a method and a device for rehabilitating concrete layers where a formation of carbonate has occurred, especially in connection with reinforced concrete and brick wall constructions, such as buildings, pilings, docks and supporting brick walls.
In these and also in other types of concrete constructions reinforcement steel is used in order to increase the strength. The concrete protects the steel against corrosion through the highly alkaline environment that normally exists in the concrete. Absorption of acidic gases, mainly carbon dioxide, and in a less degree sulphur dioxide and sulphur trioxide from the atmosphere, leads to an acidifying of the concrete, and the alkalinity will be reduced. When the pH of the concrete is reduced to about 9.5 the imbedded steel is no longer protected, and corrosion starts. If at the same time chlorides are present, the corrosion starts at higher pH-values than 9.5.
This change in the concrete, that is called formation of carbonate, may lead to corrosion of the reinforcement steel which creates breaking or blasting of the outer layer of the concrete. This produces a certain risk of accident or damage, especially in connection with buildings. It will also weaken the concrete construction.
Such damage to concrete construction has reached the point of being a serious economical and technical problem. Traditional repair is based on sandblasting and/or removal of the concrete layer where formation of carbonate has occurred by cutting it away, cleaning and optionally applying an anticorrosion treatment to the steel, followed by the casting or applying of new concrete or mortar.
There exist materials, that when they are applied to concrete surfaces help to reduce the rate of formation of carbonate in that the concrete's diffusion resistance against gases is increased. However, such materials can not rehabilitate concrete where formation of carbonate has already occurred.